This invention relates generally to transmitters and/or modulation for encoding angular position as a polarization state of the energy along a selectable one of a plurality of dimensions across the beam. More particularly, it relates to such devices which allow for the rapid change of the encoded dimension, for example, between the pitch and yaw dimensions, by electro-optical control means.
My U.S. Pat. No. 4,030,686; entitled "POSITION DETERMINING SYSTEMS"; and assigned to a common assignee; includes a transmitter for transmitting energy encoded such that the polarization states of the energy vary across the beam; and a receiver which responds to the polarization of the received energy to provide signals indicative of the relative position of an object within the beam.
According to one of the preferred embodiments disclosed in my just referenced U.S. Pat., the transmitter includes means for encoding the beam such that the polarization varies from elliptical polarization of a first rotational sense at one edge of the beam to linear polarization at the beam's center through elliptical polarization of the opposite sense at the opposite edge of the beam. The term "elliptical polarization" includes circular polarization as a special case thereof.
In my said prior patent polarization encoding across the beam was implemented by means of a laser unit that applies linearly polarized light to a wedge of birefringent material such as crystalline quartz. The polarization of the incident laser energy is oriented at 45.degree. to the optical axis of the wedge whereby the wedge decomposes the input light into two components one of which is along and the other perpendicular to the optical axis of the wedge. In passing through the wedge one of the light components is phase shifted with respect to the other and the configuration of the wedge is such that the phase shift is .+-.90.degree. at the edges of the beam. With this arrangement right-handed circular polarization is encoded at one beam edge and left-handed circular polarization at the other. The light transmitted through the center of the wedge has substantially no relatively phase shift except for an integral number of half wavelengths, between the orthogonal components thereof, and its polarization state is substantially the same or orthogonal to that of the input light to the wedge. The output light from the wedge is passed through a diverger lens which expands and shapes the beam, e.g. to produce a conical beam.
In accordance with the systems disclosed in my above cited U.S. patent, position information along a second dimension across the beam is obtained by rotating the wedge in its optical plane and transmitting a second pulse, or by using parallel transmission channels each of which is associated with a respective dimension across the beam.